For a given binary system at constant temperature and pressure, the molar volume (in $m^{3}$/mol) is given by: $v=30x_{A}+20x_{B}+x_{A}x_{B}\left ( 15x_{A} -7x_{B}\right )$, where $x_{A}$ and $x_{B}$ are the mole fraction of components $A$ and $B$, respectively. The volume change of mixing $\Delta v_{mix}$ (in $m{3}$/mol) at $x_{A}=0.5$ is _______________ (rounded off to one decimal place).